"Fast Fourier Transform" for Oscilloscope Frequency Domain Analysis

Many of today's digital oscilloscopes include a "Fast Fourier Transform" (FFT) for frequency domain analysis. This feature is particularly useful for oscilloscope users who have limited or no spectrum analyzer access but occasionally need to perform frequency domain characterization. A full oscilloscope FFT is a cost-effective, space-saving alternative to a dedicated spectrum analyzer.

The purpose of an oscilloscope's "Fast Fourier Transform" (FFT) function and various other math functions is to verify digital and RF designs. For example, an oscilloscope's FFT function can quickly highlight the frequency content of a noise signal coupled into the power supply voltage rail. This can help determine the source of this noise signal. This is important because such signals can become noise in other parts of the design, reduce signal margins, and it may be necessary to resolve the problem before the prototype can move forward. The FFT spectrum view can also help verify that the proper pulse characteristics and modulation are present when observing RF signals. The time-gated FFT can further evaluate the spectral content of the signal, such as what frequency the RF pulse will appear in certain situations. Math functions such as "Measurement Trend" in the frequency measurement section can quickly verify that the modulation is correct, such as a linear modulated chirp signal in an RF pulse train.